The hydrogenation of unsaturated polymers is very well known. In many polymer hydrogenation processes, a homogeneous, transition metal complex is used as a hydrogenation catalyst. The efficiency of the catalyst, particularly if it contains rhodium or ruthenium, may be improved by the presence of certain phosphine molecules. For example, U.K. 1,558,491 teaches the selective hydrogenation of unsaturated polymers, using a rhodium-based catalyst. The examples of this patent also illustrate that the catalyst is effectively used in the presence of 10 parts by weight of additional triphenyl phosphine per 100 parts of polymer. After the hydrogenation process, the hydrogenated polymer is recovered from the solution. However, because phosphine has a certain affinity for the hydrogenated polymer, the use of the phosphine can cause phosphine residues in the recovered hydrogenated polymer. Furthermore, there is some indication that phosphines cause problems with polymer vulcanization.
Thus, it is known that the use of additional phosphine can improve the efficiency of certain polymer hydrogenation catalysts, but a cost associated with this use is the deposition of phosphine residues in the hydrogenated polymer. Since there is a strong desire to maximize catalyst efficiency, for reasons which include process economy and product purity, there is a resulting need for a process to remove phosphine from the hydrogenated polymer solution.
It is an object of the present invention to provide a process for treating a solution which contains a hydrogenated polymer and a phosphine residue.
The present invention provides a process for treating a solution containing a hydrogenated polymer and a phosphine residue, the process comprising:
i) forming a phosphine-derived precipitate by adding to the solution an organo-halide reagent of the formula R--X where R is selected from phenoxy, C.sub.1-10 alkyl, C.sub.1-10 alkoxy, allyl and ara-alkyl, X is selected from bromine, chlorine and iodine, and PA0 ii) mechanically removing the precipitate.